ISSN:
0360-6376
Keywords:
Physics
;
Polymer and Materials Science
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
The binding of two ionic azo dyes (4-phenylazo-1-naphthol mono-and disulfonate) and a fluorescent probe (2-p-toluidinonaphthalene-6-sulfonic acid, TNS) to poly(vinylpyrrolidone) (PVP) was studied to obtain information on the nature of the interaction, binding isotherm, and binding site. Sorption of the dyes followed a Langmuir isotherm only at low polymer saturation. Apparent cooperativity in binding was seen at higher saturation. The polymer had a higher intrinsic binding constant but lower binding capacity for the doubly charged dye than for the structurally similar singly charged dye. Both dyes consisted of tautomeric mixtures of hydrazone and azonaphthol forms in equilibrium in the bound and unbound state. The preferential binding of the azonaphthol tautomer of the disulfonate was highly exothermic and accompanied by an entropy decrease. The binding of the hydrazone form was less favored by 1.8 kcal/mol, was weakly exothermic, and accompained by an entropy increase. Increased preference for the azonaphthol tautomer accompanied chain extension from charging the polymer. Chain extension had no effect on the emission frequency of bound TNS. Large differences in binding capacities for similarly charged dyes indicated the existence of specific dye-site interactions. Arguments are presented against nonspecific hydrophobic interactions as predominant forces responsible for binding.
Additional Material:
6 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/pol.1981.170191006
